The objectives of this study are to identify and characterize subpopulations of human lymphocytes and to attempt to define their role in the pathogenesis of rheumatic diseases. Specifically, DNA-binding lymphocytes will be identified using autoradiography in normal people and patients with systemic lupus erythematosus (SLE). Their number will be correlated with disease activity and anti-DNA antibody. These DNA-binding lymphocytes will be identified as B, T or "null" cells using purified cell populations prepared by Ficoll-gradient separation of appropriately prepared sheep erythrocyte rosettes or by passage of cells over a plastic bead column. Antibody induced cell mediated cytotoxicity (AIC) of peripheral lymphocytes will be studied using radioactive chromium release from antibody-coated chicken erythrocytes. AIC activity will be studied in patients with SLE, rheumatoid arthritis, and other connective tissue disorders. The cell subpopulation responsible for AIC will be studied using purified cell populations of B, T or "null" cells. Finally, an "in vitro" assay for transfer factor (TF) will be established. The cell subpopulation upon which TF acts and its possible mechanism of action will be studied.